nbdkit

 nbdkit [-f] [-g GROUP] [-i IPADDR] [-P PIDFILE] [-p PORT]
        [-r] [-s] [-U SOCKET] [-u USER] [-v] [-V]
        PLUGIN.so [key=value [key=value [...]]]

"nbdkit" is both a toolkit for creating Network Block Device (NBD) servers from "unconventional" sources and the name of an NBD server.

To create a new block device source, all you have to do is write a few glue functions. The liberal licensing of nbdkit is meant to allow you to link nbdkit with proprietary libraries or include nbdkit in proprietary code.

If you want to write an nbdkit plugin, you should read nbdkit-plugin(3).

Several plugins may be found in "LIBDIR/nbdkit/plugins" where "LIBDIR" is set at compile time and might be a path such as "/usr/lib", "/usr/lib64" or "/usr/local/lib".

Serve file "disk.img" on port 10809:

 nbdkit .../plugins/nbdkit-file-plugin.so file=disk.img

Run the example1 plugin and connect to it using guestfish(1):

 nbdkit .../plugins/nbdkit-example1-plugin.so
 guestfish --ro -a nbd://localhost

Run the example3 plugin and connect to it using guestfish(1):

 nbdkit .../plugins/nbdkit-example3-plugin.so size=1G
 guestfish --ro -a nbd://localhost

To display usage information about a specific plugin:

 nbdkit --help .../plugins/nbdkit-example1-plugin.so

--help

Display brief command line usage information and exit.

-f

--foreground

--no-fork

Don't fork into the background.

-g GROUP

--group GROUP

Change group to "GROUP" after starting up. A group name or numeric group ID can be used.

The server needs sufficient permissions to be able to do this. Normally this would mean starting the server up as root.

See also -u.

-i IPADDR

--ip-addr IPADDR

--ipaddr IPADDR

Listen on the specified interface. The default is to listen on all interfaces. See also -p.

-P PIDFILE

--pid-file PIDFILE

--pidfile PIDFILE

Write "PIDFILE" (containing the process ID of the server) after nbdkit becomes ready to accept connections.

If the file already exists, it is overwritten. nbdkit does not delete the file when it exits.

-p PORT

--port PORT

Change the TCP/IP port number on which nbdkit serves requests. The default is 10809. See also -i.

-r

--read-only

--readonly

The export will be read-only. If a client writes, then it will get an error.

Note that some plugins inherently don't support writes. With those plugins the -r option is added implicitly.

Copy-on-write (or "snapshot") functionality is not supported by this server. However if you are using qemu as a client (or indirectly via libguestfs) then it supports snapshots.

-s

--single

--stdin

Don't fork. Handle a single NBD connection on stdin/stdout. After stdin closes, the server exits.

You can use this option to run nbdkit from inetd, systemd or similar superservers; or just for testing; or if you want to run nbdkit in a non-conventional way.

This option implies --foreground.

-U SOCKET

--unix SOCKET

Accept connections on the Unix domain socket "SOCKET" (which is a path).

nbdkit neither creates nor deletes this socket. You should create the socket and set the desired permissions and ownership before running the server.

-u USER

--user USER

Change user to "USER" after starting up. A user name or numeric user ID can be used.

The server needs sufficient permissions to be able to do this. Normally this would mean starting the server up as root.

See also -g.

-v

--verbose

Enable verbose messages.

It's a good idea to use -f as well so the process does not fork into the background (but not required).

-V

--version

Print the version number of nbdkit and exit.

After specifying the plugin name you can (optionally, it depends on the plugin) give plugin configuration on the command line in the form of "key=value". For example:

 nbdkit .../plugins/nbdkit-file-plugin.so file=disk.img

To list all the options supported by a plugin, do:

 nbdkit --help .../plugins/nbdkit-file-plugin.so

nbdkit-plugin(3), nbdkit-example1-plugin(1), nbdkit-example2-plugin(1), nbdkit-example3-plugin(1), nbdkit-file-plugin(1), nbdkit-gzip-plugin(1), nbdkit-libvirt-plugin(1), nbdkit-vddk-plugin(1). nbdkit-xz-plugin(1).

Richard W.M. Jones

Copyright (C) 2013 Red Hat Inc.

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

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